1. Field of the Invention
The present invention relates to an electrocardiograph system comprising an electrocardiograph recorder and a printer, and particularly to a data transfer system between a small portable electrocardiograph recorder and an electrocardiogram printer.
2. Description of the Related Art
In conventional portable (holder) electrocardiographs, after an electrocardiogram is magnetically recorded on an electrocardiogram recording medium for 24 hours using a magnetic tape, the electrocardiogram is analyzed by a private analysis apparatus while being reproduced thereby, and the analytical results are printed. Such an electrocardiograph system has the faults that analysis and printing require much time and that a magnetic recording/reproducing system causes distortion in the waveform measured. The electrocardiograph system also has the problems that since analysis is performed by high-speed reproduction,-analysis cannot be performed for a sufficient time with high accuracy, and that the apparatus used is limited in reduction in its size and is expensive.
In addition, an electrocardiograph system has recently been developed in which the body of a portable electrocardiograph recorder contains a solid-state (semiconductor) memory and a microcomputer so that the electrocardiogram is analyzed in real time by the microcomputer during measurement for 24 hours, and the analytical results and the electrocardiogram waveform are recorded on the solid-state (semiconductor) memory. Such a system comprising a portable electrocardiograph recorder having a body which contains a memory generally employs a data transfer method in which a connector attached to the body of a portable electrocardiograph recorder is electrically connected to a connector attached to the printer and having electrical contact points when the electrocardiogram data recorded on the memory is output to a printer. However, this system has the problems that an increase in number of connections causes deterioration in the reliability because the connector has a mechanical portion, and that since there is an electrical connection, a human body is in danger if being connected to the body of the portable electrocardiograph recorder.
On the other hand, JPA 59-212949 (laid open to public on Dec. 1, 1984; corresponding U.S. Pat. No. 4,720,636) discloses electro-magnetic couplings for transferring electric power, clock and data between an IC card and a card processor. In JPA 59-212949, the electric power and clock are transferred by a common contact point, and the data is transferred by two contact points which are independently provided in the transmitting and receiving directions.
However, although the common use of the contact point for the electric power and clock causes no danger of mixing noises having different frequencies because the transfer frequency of the electric power is the same as that of the clock, the common use produces an unstable factor during receiving of the clock because the magnetic signal is distorted by a variation in the load. Further, since the area and the number of turns of a coil is increased in order to connect magnetically and efficiently more electric power, the inductance of coil is increased and it results in that the self-induction voltage is increased and that the current flowing through coil is reduced as the transfer frequency is high. Therefore, the common use of the contact point for the electric power and clock limits the setection of the transfer frequency of clock.